This invention relates generally to optical temperature measuring techniques, and, more specifically, to devices and techniques for measuring the temperature of a surface of an article by contacting its surface during processing.
There has been a great deal written about various optical temperature measuring techniques, both in patents and the technical literature, as well as many commercial products utilizing this technology. In one aspect of this technology, a luminescent material is used as a temperature sensor because certain aspects of its luminescence are temperature dependent. Typically in the form of a sensor at the end of a fiber optic cable, the luminescent material is excited to luminescence by sending excitation radiation of one wavelength to the sensor through the optical fiber, and the resulting luminescence at a different wavelength is photo-detected after passing back along the optical fiber. The detected signal is then processed to determine the temperature of the luminescent material in the sensor. Basic concepts of luminescent temperature sensing, as well as many different forms of sensors, are described in U.S. Pat. No. 4,448,547. The measurement of the decay time of the luminescence after termination of an excitation pulse, as a measurement of temperature, is described in U.S. Pat. No 4,652,143. Commercial products adopted the decay time measurement technique as a good measurement of temperature.
Applications of these luminescent sensor measurement techniques are numerous, including the measurement of surface temperature. U.S. Pat. No. 4,752,141 describes an elastomeric luminescent sensor at the end of an optical fiber that deforms as it is urged against a surface being measured in order to establish good thermal communication. An alternative use of a thin non-metallic disc with a layer of luminescent material between it and the end of an optical fiber is also described. One advantage and focus of luminescent temperature measurement techniques has been for applications in environments having strong electric and/or magnetic fields and the like, where metal sensors cannot be relied upon to provide accurate results since the metal is heated as a result of the field.
Another optical temperature measuring technique relies upon the infrared emissions of a black-body sensor, or one having the characteristics of a black-body. An example of such a system, generally used to measure higher temperatures than measured with luminescent sensors, is described in U.S. Pat. No. 4,750,139. The sensor is a black-body emitter formed at the end of an optical fiber. U.S. Pat. No. 5,183,338 describes several forms of a fiber optic sensor that includes both luminescent and black-body temperature measuring elements. Each of the foregoing identified patents is expressly incorporated herein in its entirety by this reference.
There are also many other optical temperature sensing techniques that have been described in patents and the literature, as well as being used commercially. But the luminescent and black-body techniques have generally been preferred over those others.
Briefly, an optical temperature sensor is formed on an end of an optical radiation wave guide, such as an optical fiber, which may use a luminescent, black-body or other existing optical temperature sensitive material, in a form especially adapted for measuring the temperature of a surface, particularly, by way of example, a surface of a semiconductor wafer, flat panel display or other substrate being processed within a processing chamber. A rigid support for the temperature sensitive material, such as a cap in which the material is held on an inside, is positioned adjacent the wave guide end with a space normally between them. A resilient element urges the cap away from the wave guide end, at least in response to the cap being pushed toward the wave guide end when the sensor being brought into contact with the surface being measured. This provides very close contact with the surface, resulting in good thermal transfer and equilibrium between the surface and the temperature sensitive material. There are several useful forms of the temperature sensitive material support and resilient element, which may be formed as one or made separate. One specific form uses a closed end bellows element that both provides a cap having the temperature sensitive material on its inside and the resilient element in its side walls, the optical fiber being inserted into the bellows from an open end.
The sensors of the present invention have application in a number of different environments, including very hostile environments. Sensors of the present invention operate within a chamber having a high vacuum, a chemical bath chamber, environments with extreme hot or cold, or those with high levels of radio frequency, microwave or other electromagnetic radiation bands.
A primary reason for wanting to know the temperature of a substrate being processed is to allow its temperature to be set or varied as desired by making suitable adjustments to the processing equipment. According to another aspect of the present invention, instead of measuring the temperature of the actual substrates being processed, however, a test substrate or other object being processed is provided with at least one optical temperature sensor formed in a surface of the substrate. The test substrate is then periodically or occasionally positioned in the processing chamber in place of an actual substrate being processed, during which time the processing equipment is calibrated to provide the desired substrate temperature during processing. Such a sensor preferably includes optical temperature sensing material imbedded into a small area of the surface behind a protective transparent window. The sensor is viewed by directing optical radiation through the window.
Additional aspects, features and advantages of the present invention are included in the following description of exemplary embodiments thereof, which description should be taken in conjunction with the accompanying drawings.